Kanegae Marília P P, da Fonseca Luiz Marcos, Brunetti Iguatemy L, Silva Sueli de Oliveira, Ximenes Valdecir F
Departamento de Análises Clínicas, Faculdade de Ciências Farmacêuticas, Universidade Estadual Paulista, Araraquara, SP, Brazil.
Biochem Pharmacol. 2007 Aug 1;74(3):457-64. doi: 10.1016/j.bcp.2007.05.004. Epub 2007 May 10.
Redox processes are involved in the mechanism of action of NADPH oxidase inhibitors such as diphenyleneiodonium and apocynin. Here, we studied the structure-activity relationship for apocynin and analogous ortho-methoxy-substituted catechols as inhibitors of the NADPH oxidase in neutrophils and their reactivity with peroxidase. Aiming to alter the reduction potential, the ortho-methoxy-catechol moiety was kept constant and the substituents at para position related to the hydroxyl group were varied. Two series of compounds were employed: methoxy-catechols bearing electron-withdrawing groups (MC-W) such as apocynin, vanillin, 4-nitroguaiacol, 4-cyanoguaiacol, and methoxy-catechol bearing electron-donating groups (MC-D) such as 4-methylguaiacol and 4-ethylguaiacol. We found that MC-D were weaker inhibitors compared to MD-W. Furthermore, the radicals generated by oxidation of MC-W via MPO/H(2)O(2), but not for MC-D, were able to oxidize glutathione (GSH) as verified by the formation of thiyl radicals, depletion of GSH, and recycling of the ortho-methoxy-catechols during their oxidations. The capacity of oxidizing sulfhydryl (SH) groups was also verified when ovalbumin was incubated with MC-W, but not for MC-D. Since the effect of apocynin has been correlated with inactivation of the cytosolic fractions of the NADPH oxidase complex and its oxidation during the inhibitory process develops a special role in this process, we suggest that the close relationship between the reactivity of the radicals of MC-W compounds with thiol groups and their efficacy as NADPH oxidase inhibitor could be the chemical pathway behind the mechanism of action of apocynin and should be taken into account in the design of new and specific NADPH oxidase inhibitors.
氧化还原过程参与了二苯撑碘鎓和夹竹桃麻素等NADPH氧化酶抑制剂的作用机制。在此，我们研究了夹竹桃麻素及类似的邻甲氧基取代儿茶酚作为中性粒细胞中NADPH氧化酶抑制剂的构效关系及其与过氧化物酶的反应活性。为了改变还原电位，邻甲氧基儿茶酚部分保持不变，与羟基相关的对位取代基则有所不同。使用了两个系列的化合物：带有吸电子基团的甲氧基儿茶酚（MC-W），如夹竹桃麻素、香草醛、4-硝基愈创木酚、4-氰基愈创木酚，以及带有供电子基团的甲氧基儿茶酚（MC-D），如4-甲基愈创木酚和4-乙基愈创木酚。我们发现，与MC-W相比，MC-D是较弱的抑制剂。此外，通过MPO/H₂O₂氧化MC-W产生的自由基能够氧化谷胱甘肽（GSH），而MC-D产生的自由基则不能，这通过硫自由基的形成、GSH的消耗以及邻甲氧基儿茶酚在氧化过程中的循环得以证实。当卵清蛋白与MC-W孵育时，氧化巯基（SH）基团的能力也得到了证实，但MC-D则没有。由于夹竹桃麻素的作用与NADPH氧化酶复合物胞质部分的失活相关，且其在抑制过程中的氧化在该过程中发挥了特殊作用，我们认为MC-W化合物自由基与硫醇基团的反应活性与其作为NADPH氧化酶抑制剂的效力之间的密切关系可能是夹竹桃麻素作用机制背后的化学途径，在设计新型特异性NADPH氧化酶抑制剂时应予以考虑。
